1. Field of the Invention
This invention relates to polyolefin composites, particularly to processes for drying fillers and catalytically-active fillers for use in preparing homogeneous polyolefin composites.
2. Technical Background
U.S. Pat. Nos. 4,187,210, 4,097,447, 4,126,647 and 4,104,243 to Howard, and U.S. Pat. No. 4,151,126 to Adelman & Howard, disclose composites of polyolefins, including ultrahigh molecular weight polyethylene, with a variety of finely divided particulate inorganic filler compounds, including alumina, calcium carbonate, kaolinite clay, mica and conductive carbon, and organic filler materials such as polyacrylonitrile, wherein the composites comprise at least about 25% by weight of filler. These patents, together with U.S. Pat. No. 4,104,243 (Howard), also disclose methods of preparing composites which permit relatively high loadings of filler without sacrifice of essential physical properties. In these processes, ethylene is polymerized on the surface of catalytically acitive filler particles. The resulting composites are substantially free of polymer-free filler and of filler-free polymer.
In the processes of the aforementioned patents, filler materials having neutral-to-acidic surfaces or chemically modified to have such surfaces, are dispersed in hydrocarbon solvents and rendered catalytically active by treatment with selected transition metal compounds. It is essential for the filler compounds to be "dry", that is, substantially free of water and other polar organic compounds such as alcohols which can interfere with the attachment of the transition metal catalysts to the filler surfaces and/or with the olefin polymerization step. Filler drying may be required with as-received filler materials, or after one or more of the various treatments described in the aforementioned patents, to provide adequate surface acidity and/or transition metal content.
In conventional drying procedures, including those practiced in the aforementioned patents, fillers are often heated for long periods (12-24 h) at temperatures of 100.degree. to about 300.degree. C. in a stream of inert gas such as nitrogen; typically a flow of about 20-800 liter/h is employed. Such drying normally requires special apparatus, separate from the equipment used for preparing catalytically active filler.
For commercial practice there is a need for conducting all steps in the preparation of catalytically active filler in situ, i.e., in the same vessel, and for eliminating the costly use of large volumes of gas during drying steps. Drying (water removal) of liquids and solids by azeotropic distillation employing various organic liquids is known.
U.S. Pat. Nos. 4,780,438 and 4,780,439 disclose a method of preparing a supported catalyst for polymerizing olefins wherein magnesium chloride support material is dissolved in ethanol and the ethanol solution is dried by azeotropic distillation of an ethanol/water mixture. The magnesium chloride is subsequently precipitated from ethanol solution and reacted with a titanium compound to form the supported catalyst.
Kirk-Othmer Encyclopedia discloses water removal from solids by adding an "entrainer" such as benzene or toluene and azeotropically distilling the water; azeotropic drying at lower temperatures is cited as a way to avoid chemical by-products.
U.S. Pat. No. 3,979,504 discloses a process for preparing a high-surface area alumina comprising drying an aqueous slurry of the alumina by admixture with an organic solvent and distilling a solvent/water azeotrope. The organic solvent should have a lower surface tension than water; C.sub.2-4 alcohols are disclosed as suitable.
British Patent 1,120,402 discloses a method of drying ion-exchange desiccants by mixing the water-laden resin with an azeotrope-forming halogenated hydrocarbon and distilling a hydrocarbon/water azeotrope. The desired boiling range for the azeotrope at atmospheric pressure is given as 50.degree.-165.degree. C., preferably 85.degree.-125.degree. C.
The present invention provides an economical in-situ (one pot) process for preparing catalytically active fillers for olefin polymerization comprising dispersing the fillers, which may have been previously treated to acidify the filler surfaces, in a non-solvent liquid hydrocarbon and distilling a water-containing azeotrope.